A 2,3-dihydroimidazo[2,1-b]oxazole compound represented by Formula (1) below or a salt thereof is useful as an antitubercular agent (Patent Literatures 1, 2 and 3).

In Formula (1), R1 is a hydrogen atom or lower-alkyl group;
R2 is a 1-piperidyl group substituted at the 4-position with a substituent selected from
(A1a) a phenoxy group substituted on the phenyl moiety with one or more halogen-substituted lower-alkoxy groups,
(A1b) a phenoxy-substituted lower-alkyl group substituted on the phenyl moiety with one or more halogen-substituted lower-alkyl groups,
(A1c) a phenyl-substituted lower-alkoxy lower-alkyl group substituted on the phenyl moiety with halogen,
(A1d) a phenyl-substituted lower-alkyl group substituted on the phenyl moiety with one or more halogen-substituted lower-alkoxy groups,
(A1e) an amino group substituted with a phenyl group substituted with one or more halogen-substituted lower-alkoxy groups, and a lower-alkyl group, and
(A1f) a phenyl-substituted lower-alkoxy group substituted on the phenyl moiety with one or more halogen-substituted lower-alkoxy groups; and
n is an integer from 1 to 6.
These patent literatures disclose Reaction Schemes A and B below as the processes for producing the aforementioned 2,3-dihydroimidazo[2,1-b]oxazole compound.
wherein R1 is a hydrogen atom or lower-alkyl group; R2 is a substituted piperidyl group or a substituted piperazinyl group; and X1 is a halogen atom or a nitro group.
wherein X2 is a halogen or a group causing a substitution reaction similar to that of a halogen; n is an integer from 1 to 6; and R1, R2 and X1 are the same as in Reaction Scheme A.
An oxazole compound represented by Formula (1a):
i.e., 2-methyl-6-nitro-2-{4-[4-(4-trifluoromethoxyphenoxy)piperidin-1-yl]phenoxymethyl}-2,3-dihydroimidazo[2,1-b]oxazole (hereunder, this compound may be simply referred to as “Compound 1a”) is produced, for example, by the method shown in the Reaction Scheme C below (Patent Literature 3). In this specification, the term “oxazole compound” means an oxazole derivative that encompasses compounds that contain an oxazole ring or an oxazoline ring (dihydrooxazole ring) in the molecule.

However, the aforementioned methods are unsatisfactory in terms of the yield of the objective compound. For example, the method of Reaction Scheme C allows the objective oxazole Compound (1a) to be obtained from Compound (2a) at a yield as low as 35.9%. Therefore, alternative methods for producing the compound in an industrially advantageous manner are desired.